Target value control method for transmission power control, base station control device and mobile station used for the same

ABSTRACT

When a reception data block has no error (S 1 : NO), a target SIRt is updated by a reduction amount according to the count CBN having no reception data block error continuously (S 3 ). That is, when the CBN is 1 to 100, reduction is made by ΔSIRt×BLERt/(1−BLERt) (Here, the BLERt is a target block error ratio). When the CBN is 101 to 200, reduction is made by 2×ΔSIRt×BLERt/(1−BLERt). When the CBN is 201 to 300, reduction is made by 3×ΔSIRt×BLERt/(1−BLERt). Thus, it is possible to rapidly reduce the reception level.

TECHNICAL FIELD

The present invention relates to a target value control method fortransmission power control and a base station control device and mobilestation used for the target value control method and, more particularly,to an improvement of a target transmission power value change controlmethod of controlling the transmission power of a radio channel betweena mobile station and a base station in a mobile communication system.

BACKGROUND ART

A transmission power control method in a conventional mobilecommunication system will be explained. As shown in FIG. 1, the mobilecommunication system generally comprises a mobile station 1, radio basestations (to be simply referred to as base stations hereinafter) 2 and3, and a base station control device 4 which controls these basestations.

Power control of the up link (UL) will be explained. The base stationmeasures an SIR (Signaling Interference Ratio) equivalent to a UL radioreception level, and compares the SIR with a UL target SIR (targettransmission power value) sent from the base station control device 4.If the measured SIR is lower than the target SIR, the base stationinstructs the mobile station 1 via the down link (DL) to increase the ULtransmission power by a step designated in advance. To the contrary, ifthe measured SIR is higher than the target SIR, the base stationinstructs the mobile station via the DL to decrease the UL transmissionpower by a step designated in advance.

The base station control device 4 receives UL radio qualities (includingreception data qualities) sent from the base stations 2 and 3, andcalculates information (target SIR) for controlling to keep the ULreception quality constant. The target SIR calculation method will beexplained below. In the following description, the target SIR will beabbreviated to SIRt.

In order to maintain the BLER (BLock Error Ratio) of a reception datablock at a constant value (target BLER: to be simply referred to asBLERt hereinafter), when the reception data block has an error, the SIRtis increased by ΔSIRt. That is, the SIRt is updated to (SIRt+ΔSIRt). Ifthe reception data block does not have any error, the SIRt is decreasedby ΔSIRt×BLERt/(1−BLERt). That is, the SIRt is updated to(SIRt−ΔSIRt×BLERt/(1−BLERt)).

More specifically, the SIRt serving as a target SIR is updated andcontrolled as shown in FIG. 9. A required SIR (dotted line in FIG. 9) is5 dB, ΔSIRt is 0.5 dB, and the BLERt as a target BLER is 0.01 (1%). Inthis case, if the SIRt becomes lower than 5 dB, an error occurs inreception data, and the SIRt increases by ΔSIRt=0.5 dB. The SIRt isequal to or higher than 5 dB during (1−BLERt)/BLERt=99 (corresponding to99 blocks), and becomes lower than 5 dB again upon the lapse of a timecorresponding to the 99 blocks (in FIG. 9, the SIRt seems to be on the5-dB dotted line, but in practice, is slightly below the 5-dB dottedline).

Then, an error occurs in reception data, the SIRt becomes higher againby ΔSIRt=0.5 dB, and the same operation is repeated. Transmission powercontrol is executed so that the radio quality of the up link (UL)satisfies a target BLER (BLERt). The above-described transmission powercontrol method is disclosed in, e.g., Ashwin Sampath et al., “On SettingReverse Link Target SIR in a CDMA System”, Vehicular TechnologyConference, 1997 IEEE 47th, Vol. 2, 4-7 May, 1997, pp. 929-933.

The transmission power control method in the conventional mobilecommunication system suffers the following problems. That is, when arequired reception level for obtaining a required radio quality dropsupon a change in radio propagation environment, the reception levelcannot be quickly decreased following the drop of the required receptionlevel.

In general, as the moving speed of a mobile station changes, therequired SIR also changes. For example, when the mobile station changesfrom a high-speed moving state to a low-speed moving state within ashort time, the required SIR changes from a high level to a low level.When the required SIR changes from 15 dB to 5 dB, as represented by adotted line in FIG. 10, the above-described conventional methodgradually decreases the target SIR (SIRt), as represented by a solidline in FIG. 10, and cannot quickly decrease the reception level. Whilethe reception level drops, communication is done at excessive power withan excessive communication quality, wasting power consumption.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a target valuecontrol method for transmission power control in a mobile communicationsystem in which, when a reception level required to obtain a requiredreception quality drops upon a change in radio propagation environment,the reception level can be quickly decreased, and even if the receptionlevel is quickly decreased, the reception quality does not degrade, anda base station control device and mobile station used for the targetvalue control method.

A target value control method according to the present invention ischaracterized by comprising the first step of changing and controlling atarget value used in transmission power control of a radio channel inorder to maintain the radio channel between a mobile station and a basestation at a predetermined reception quality, and the second step ofvariably controlling a decrease amount of the target value in accordancewith the reception quality of the radio channel.

A base station control device according to the present invention ischaracterized by comprising selection/synthesis means for receiving froma base station a reception quality of a radio up link from a mobilestation to the base station, and target value control means for changinga target value used in transmission power control of the radio up linkin the base station, variably controlling a decrease amount of thetarget value in accordance with the reception quality, and notifying thebase station of the changed target value in order to maintain the radioup link at a predetermined reception quality.

A mobile station according to the present invention is characterized bycomprising down-link SIR measurement means for measuring an SIR(Signaling Interference Ratio) of a radio down link from a base stationto the mobile station, down-link quality measurement means for measuringa reception quality of the radio down link, target value control meansfor changing a target value used in transmission power control of theradio down link to the base station, and variably controlling a decreaseamount of the target value in accordance with the reception quality inorder to maintain the radio down link at a predetermined receptionquality, and means for instructing the base station to increase/decreasetransmission power of the radio down link in accordance with acomparison result between the updated target value and the SIR.

According to the present invention, a program for causing a computer toexecute operation of a base station control device which changes andcontrols a target value for transmission power control of a radio uplink from a mobile station to a base station in order to maintain thetarget value at a predetermined reception quality is characterized bycausing the computer to execute the step of variably controlling adecrease amount of the target value in accordance with the receptionquality of the radio up link.

According to the present invention, another program for causing acomputer to execute operation of a mobile station which changes andcontrols a target value for transmission power control of a radio downlink from a base station in order to maintain the target value at apredetermined reception quality is characterized by causing the computerto execute the step of variably controlling a decrease amount of thetarget value in accordance with the reception quality of the radio downlink.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view of a schematic system configuration to which anembodiment of the present invention is applied;

FIG. 2 is a functional block diagram of each device in FIG. 1;

FIG. 3 is a flowchart of the first embodiment of the present invention;

FIG. 4 is a graph showing an example of a change in target SIR in thefirst embodiment of the present invention;

FIG. 5 is a flowchart of the second embodiment of the present invention;

FIG. 6 is a graph showing an example of a change in target SIR in thesecond embodiment of the present invention;

FIG. 7 is a flowchart of the third embodiment of the present invention;

FIG. 8 is a graph showing an example of a change in target SIR in thethird embodiment of the present invention;

FIG. 9 is a graph showing an example of a change in target SIR when arequired SIR is 5 dB; and

FIG. 10 is a graph showing an example of a change in target SIR in theprior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings.

[Mobile Communication System]

FIG. 1 is a schematic view of a mobile communication system to which anembodiment of the present invention is applied. The mobile communicationsystem comprises a mobile station 1, base stations 2 and 3, and a basestation control device 4. FIG. 2 is a functional block diagram of themobile station 1, base stations 2 and 3, and base station control device4 in FIG. 1. The base stations 2 and 3 have the same configuration, andthe functional block of only the base station 2 is illustrated in FIG.2.

[Base Station]

The base station 2 will be explained with reference to FIG. 2. Areceiver 21 receives a UL signal from the mobile station 1. An up-linkSIR measurement unit 22 measures a UL SIR from the UL reception level.An up-link target SIR & up-link SIR comparison unit 23 compares the ULSIR with a UL target SIR (UL SIRt) sent from the base station controldevice 4. When the UL SIR is lower than the UL SIRt, the up-link targetSIR & up-link SIR comparison unit 23 sends to a transmitter 26information which instructs the mobile station via the DL to increasethe UL transmission power, and when the UL SIR is higher than the ULSIRt, sends to the transmitter 26 information which instructs the mobilestation via the DL to decrease the UL transmission power.

An up-link radio quality or reception data quality measurement unit 24measures the UL radio quality or reception data quality of a signalreceived by the receiver 21, and notifies the base station controldevice 4 of the measurement result. A down-link transmission powercalculation unit 25 extracts DL transmission power instructioninformation sent from the receiver 21, calculates a UL transmissionpower in accordance with the information, and notifies the transmitter26 of the UL transmission power. The transmitter 26 transmitsinformation which instructs the mobile station to increase/decrease theUL transmission power, and performs transmission at a transmission powervalue designated by the down-link transmission power calculation unit25.

[Base Station Control Device]

The base station control device 4 will be explained. An up-link radioquality or reception data quality selection/synthesis unit 41 receivesUL radio qualities or reception data qualities sent from one or aplurality of base stations, and selects and synthesizes them. An up-linktarget SIR update unit 42 compares the selected/synthesized UL radioquality or reception data quality with a UL radio quality or receptiondata quality which satisfies a required quality set in advance. Theup-link target SIR update unit 42 updates the UL target SIR (UL SIRt) soas to satisfy the required quality, and notifies the base station of theupdated UL SIRt.

[Mobile Station]

The mobile station 1 will be explained. A receiver 11 receives adown-link signal from the base station. A down-link SIR measurement unit12 measures an SIR equivalent to a DL radio reception level. A down-linkradio quality or reception data quality measurement unit 13 measures theDL radio quality or reception data quality of a signal received by thereceiver 11, and notifies a down-link target SIR update unit 14 of themeasurement result. The down-link target SIR update unit 14 compares theDL reception quality or reception data quality with a DL radio qualityor reception data quality which satisfies a required quality set inadvance. The down-link target SIR update unit 14 updates the DL targetSIR so as to satisfy the required quality, and notifies a down-linktarget SIR & down-link SIR comparison unit 15 of the updated DL targetSIR.

The down-link target SIR & down-link SIR comparison unit 15 compares theDL SIR with a DL target SIR serving as a DL target radio receptionlevel. When the DL SIR is higher than the DL target SIR, the down-linktarget SIR & down-link SIR comparison unit 15 sends to a transmitter 17information which instructs the base station via the UL to decrease theDL transmission power, and when the DL SIR is lower than the DL targetSIR, sends to the transmitter 17 information which instructs the basestation via the UL to increase the DL transmission power. An up-linktransmission power calculation unit 16 extracts up-link transmissionpower instruction information from a signal received by the receiver 11,calculates a UL transmission power in accordance with the instructioninformation, and notifies the transmitter 17 of the UL transmissionpower. The transmitter 17 transmits, to the base station, informationwhich instructs the base station to increase/decrease the DLtransmission power, and performs transmission at a transmission powervalue designated by the up-link transmission power calculation unit 16.

First Embodiment

An update control mode of a target SIR (to be referred to as SIRt) fortransmission power control according to the first embodiment of thepresent invention will be described. First, UL transmission powercontrol will be explained. In the base station, an up-link SIRmeasurement unit 22 measures an SIR serving as a UL radio receptionlevel, and a comparison unit 23 compares the measured SIR with an SIRtserving as a UL target SIR which is sent in advance from a base stationcontrol device 4. If the SIR is lower than the SIRt as a result ofcomparison, the base station instructs a mobile station 1 via the DL toincrease the UL transmission power, and if the SIR is higher than theSIRt, instructs the mobile station 1 via the DL to decrease the ULtransmission power.

An up-link radio quality or reception data quality measurement unit 24measures a UL radio quality (also including a reception data quality),and notifies the base station control device 4 of the measurementresult. The radio quality is, e.g., error information of a receptiondata block, and will be called a BLER (Block Error Ratio). The basestation control device 4 receives UL radio qualities from a plurality ofbase stations, and an up-link target SIR update unit 42 calculates a ULtarget SIR (SIRt) serving as information for controlling to keep the ULreception quality constant.

The UL SIRt calculation method is shown in the flowchart of FIG. 3. TheUL BLER is used as a UL radio quality, and the BLER is kept at apredetermined target value (BLERt). In this case, if an error exists ina reception data block (step S1: YES), the SIRt is increased by ΔSIRt(predetermined value). That is, the SIRt is updated to SIRt+ΔSIRt (stepS2). If no error exists in the reception data block (S1: NO), the SIRtis updated to SIRt−int{1+(CBN−1)×BLERt}×ΔSIRt×BLERt/(1−BLERt) (step S3).

At this time, int{ } means a function of rounding down the decimal partinto an integer, and CBN (Continuous Block Number) represents the numberof continuous reception data blocks free from any error. For BLERt=0.01%and CBN=1 to 100, int{ }=1, and the SIRt is updated toSIRt−ΔSIRt×BLERt/(1−BLERt), similar to the prior art.

However, for CBN=101 to 200, int{ }=2, and the SIRt is updated toSIRt−2×ΔSIRt×BLERt/(1−BLERt). For CBN=201 to 300, int{ }=3, and the SIRtis updated to SIRt−3×ΔSIRt×BLERt/(1−BLERt). In other words, as thenumber of continuous reception data blocks free from any errorincreases, the SIRt decrease amount is increased. With this setting, theSIRt changes as shown in FIG. 4 under the same condition as that of theprior art shown in FIG. 10.

FIG. 4 shows an example of a change in SIRt when a required SIR changesfrom 15 dB to 5 dB, as represented by the dotted line, and no errorappears in continuous reception data blocks. As is apparent from acomparison between FIGS. 4 and 10, when the required SIR changes fromhigh level to low level, the SIRt control method according to the firstembodiment can quickly change the target SIR (SIRt) to the required SIR(5 dB in the example of FIG. 4), and can also decrease the UL receptionlevel.

Obviously, the comparison unit 23 of the base station is notified of thecalculated/updated SIRt and the SIRt is set as an up-link target SIR.

SIRt update control in UL transmission power control has been described,and next, SIRt update control in DL transmission power control will beexplained. In the mobile station 1, a down-link SIR measurement unit 12measures an SIR serving as a DL radio reception level, and a comparisonunit 15 compares the measured SIR with an SIRt serving as a preset DLtarget SIR. If the SIR is lower than the SIRt as a result of comparison,the mobile station 1 instructs a base station via the UL to increase theDL transmission power, and if the SIR is higher than the SIRt, instructsthe base station via the UL to decrease the DL transmission power.

A down-link radio quality or reception data quality measurement unit 13measures a DL radio quality (also including a reception data quality),and notifies a down-link target SIR update unit 14 of the measurementresult. The radio quality is, e.g., error information BLER of areception data block. By using the notified DL BLER, the update unit 14calculates a DL target SIR (SIRt) serving as information for controllingto keep the DL reception quality constant. This calculation methodcomplies with the same procedures as those shown in the flowchart ofFIG. 3. The comparison unit 15 is notified of the calculated/updatedSIRt, and the SIRt is set as a down-link target SIR. An example of achange in SIRt is also the same as that shown in FIG. 4.

Second Embodiment

A control mode of a target SIR (SIRt) for transmission power controlaccording to the second embodiment of the present invention will bedescribed. First, an SIRt control method in UL transmission powercontrol will be explained. An up-link quality or reception data qualitymeasurement unit 24 in a base station measures a UL BLER, and notifies abase station control device 4 of the UL BLER. The base station controldevice 4 receives UL BLERs from a plurality of base stations, and anup-link target SIR update unit 42 calculates a UL target SIR (SIRt)serving as information for controlling to keep the UL reception qualityconstant.

The UL SIRt calculation method is shown in the flowchart of FIG. 5. TheUL BLER is used as a UL radio quality, and the BLER is kept at apredetermined target value (BLERt). In this case, if an error exists ina reception data block (step S21: YES), the SIRt is increased by ΔSIRt(predetermined value) (step S22). If no error exists in reception data(S21: NO), the flow branches into the following two cases.

More specifically, a threshold Cth of the number of continuous receptiondata blocks free from any error is introduced. The SIRt update aspect ischanged between two cases: whether the CBN (Continuous Block Number)representing the number of continuous reception data blocks free fromany error is equal to or smaller than Cth/BLERt, or is larger than it.For BLERt=0.01 (1%) and Cth=2.0 (in general, 1.0 to 3.0), Cth/BLERt=200.If the CBN is equal to or lower than 200 (step S23: YES), the SIRt isupdated to SIRt−ΔSIRt×BLERt/(1−BLERt) (step S24). This is the same asthe process in the first embodiment and prior art.

If the CBN exceeds 200 (step S23: NO), the SIRt is updated to SIRt−ΔSIRt(step S25). In other words, if the number of continuous reception datablocks free from any error exceeds a predetermined threshold, the SIRtis decreased at once by a predetermined maximum amount (ΔSIRt).

FIG. 6 shows an example of a change in target SIR in the secondembodiment. The condition in FIG. 6 is the same as those in FIGS. 10 and4, and Cth/BLERt=200 (Cth=2.0).

The SIRt update method in UL transmission power control has beendescribed. For the DL, the same update operation as that described aboveis executed in a mobile station 1.

Third Embodiment

The third embodiment of the present invention will be described. Thethird embodiment is a combination of the first and second embodiments,and operation procedures of the third embodiment are shown in FIG. 7. InFIG. 7, the same reference symbols as in FIG. 5 denote the same steps.FIG. 7 is different from FIG. 5 in that, if “YES” (affirmative) in stepS23, the SIRt is updated toSIRt=SIRt−int{1+(CBN−1)×BLERt}×ΔSIRt×BLERt/(1−BLERt) (step S26), whichis the same as step S3 in FIG. 3.

FIG. 8 shows an example of a change in target SIR in the thirdembodiment. The condition in FIG. 8 is the same as those in FIGS. 10, 4,and 6, and Cth/BLERt=300 (Cth=3.0).

When the required SIR changes from 15 dB to 5 dB, as described in theabove embodiments, the simulation result exhibits BLER=0.95% in thefirst embodiment and BLER=0.99% in the second embodiment. Both of theresults satisfy the target BLER=1% (0.01).

The operation in each of the above-described embodiments can be achievedby recording operation procedures as a program on a recording medium inadvance, and reading and executing the program by a computer.

As has been described above, according to the above-describedembodiments, the change amount (decrease amount) of the target SIR iscontrolled in accordance with the number of continuous reception datablocks free from any error. As the continuous block number increases,the decrease amount is increased. Even if a reception level required toobtain a required reception quality drops upon a change in radiopropagation environment, the reception level can be quickly decreased.Since the reception level can be decreased more quickly than in theprior art, transmission at excessive power with an excessivecommunication quality can be prevented. Also, even if the receptionlevel is quickly decreased, the reception quality does not degrade.

1-19. (canceled)
 20. A target value control method characterized bycomprising: the first step of changing and controlling a target valueused in transmission power control of a radio channel in order tomaintain the radio channel between a mobile station and a base stationat a predetermined reception quality; and the second step of variablycontrolling a decrease amount of the target value in accordance with thereception quality representing an error state of reception data blocksin the radio channel, the second step comprising the third step ofvariably controlling the decrease amount in accordance with a continuousblock count by which no error occurs in the reception data blocks, thethird step comprising the fourth step of increasing the decrease amountas the continuous block count increases, and the fourth step comprisingthe step of switching the decrease amount from a small amount to a largeamount before and after the continuous block count reaches apredetermined value.
 21. A target value control method according toclaim 20, characterized in that the fourth step further comprises thestep of changing the decrease amount to a predetermined maximum amountimmediately after the continuous block count reaches the predeterminedvalue.
 22. A base station control device characterized by comprising:selection/synthesis means for receiving from a base station a receptionquality of a radio up link from a mobile station to the base station;and target value control means for changing a target value used intransmission power control of the radio up link in the base station,variably controlling a decrease amount of the target value in accordancewith the reception quality representing an error state of reception datablocks in the radio channel, and notifying the base station of thechanged target value in order to maintain the radio up link at apredetermined reception quality, wherein said target value control meansvariably controls the decrease amount in accordance with a continuousblock count by which no error occurs in the reception data blocks.
 23. Abase station control device according to claim 22, characterized in thatsaid target value control means increases the decrease amount as thecontinuous block count increases.
 24. A base station control deviceaccording to claim 23, characterized in that said target value controlmeans switches the decrease amount from a small amount to a large amountbefore and after the continuous block count reaches a predeterminedvalue.
 25. A base station control device according to claim 24,characterized in that said target value control means changes thedecrease amount to a predetermined maximum amount immediately after thecontinuous block count reaches the predetermined value.
 26. A mobilestation characterized by comprising: down-link SIR measurement means formeasuring an SIR (Signaling Interference Ratio) of a radio down linkfrom a base station to the mobile station; down-link quality measurementmeans for measuring a reception quality of the radio down link; targetvalue control means for changing a target value used in transmissionpower control of the radio down link to the base station, and variablycontrolling a decrease amount of the target value in accordance with thereception quality representing an error state of reception data blocksin the radio channel in order to maintain the radio down link at apredetermined reception quality; and means for instructing the basestation to increase/decrease transmission power of the radio down linkin accordance with a comparison result between the updated target valueand the SIR, wherein said target value control means variably controlsthe decrease amount in accordance with a continuous block count by whichno error occurs in the reception data blocks, increases the decreaseamount as the continuous block count increases, and switches thedecrease amount from a small amount to a large amount before and afterthe continuous block count reaches a predetermined value.
 27. A mobilestation according to claim 26, characterized in that said target valuecontrol means changes the decrease amount to a predetermined maximumamount immediately after the continuous block count reaches thepredetermined value.